This invention relates to a naphthalocyanine derivative, a process for producing the same, an optical recording medium using the same, and a process for producing the optical recording medium.
In recent years, it has been proposed to utilize diode laser beams for writing and reading in compact discs, video discs, liquid crystal display devices, optical reading machines, etc. and as light source for electrophotograph. For writing or reading by use of diode laser beams, a substance capable of absorbing diode laser beams, i.e., near infrared rays is indispensable.
As organic dyes which absorb near infrared rays, cyanine dyes have heretofore been well known, and metal complexes of oximes and thiols and aminated quinone derivatives are also known as dyes which absorb near infrared rays [Yuki Gosei Kagaku Kyokai Shi, vol. 43, p. 334 (1985), Shikizai Kyokai Shi, Vol. 53, p. 197 (1980), and Shikizai Kyokai Shi, vol. 58, p. 220 (1985)].
However, the cyanine dyes have a very low stability against light and hence their employment has many restrictions. The metal complexes of oximes and thiols are disadvantageous in that the metals are released from the complexes in a certain medium, resulting in loss of the ability to absorb near infrared rays. The aminated quinone derivatives are very poor in ability to absorb near infrared rays.
On the other hand, as materials capable of overcoming these problems, naphthalocyanine derivatives have recently been known, but conventional unsubstituted metal naphthalocyanines [Zhurnal Obshchei Khimii, vol. 39, p. 2554 (1969) and Mol. Cryst. Liq. Cryst. 112, 345 (1984)]are insoluble in organic solvents and hence are very difficult to purify. Recently, synthesis of naphthalocyanine derivatives soluble in organic solvents has been reported (Japanese Patent Appln. Kokai (Laid-Open) Nos. 60-23451, 60-184565, 61-215662 and 61-215663), but these naphthalocyanine derivatives have the following disadvantages. Their absorption varies greatly depending on the kind of solvent, concentration, temperature, etc., and in a solution having a high concentration or in the form of a solid film, their ability to absorb diode laser beams having a specific wavelength is greatly lowered because of broadening of their absorption spectra, and moreover the reflectance which is important when reflected light is used for reading out information recorded in an optical disc is very low in the diode laser region (780 to 830 nm).